Solid propellant systems generally comprise a plastic material in admixture with a light metal, such as aluminum or beryllium, and a metal oxide, along with conventional compounding adjuvants, such as sulfur, accelerators, anti-oxidants, anti-ozonants and activators, and particles of a solid oxidizer, such as ammonium perchlorate. The various solids and the plastic material are blended together to form a plastic mass, which is formed into shapes and cured. The cured propellant systems must have certain essential characteristics in order to perform satisfactorily. For example, the cured system must burn evenly at approximately the same rate over all exposed surfaces, be sufficiently strong to withstand stresses developed during burning, and not crack or shatter either prior to or during the burning process. It is apparent that only a propellant system having a very high degree of homogeneity can perform satisfactorily.
Solid propellant compositions are fabricated into desired shapes by moulding, extruding or pressing formulations of several solids admixed in a plastic binder material. The binder materials utilized are generally thermoplastic resins and/or resins which may be cured by chemical cross-linking reactions. High shear devices capable of separating fine-sized particles from each other are generally employed to obtain a homogeneous blend of the solids and the plastic binder prior to fabricating the blend into the shape desired.
In practice, the oxidizer provides the major portion of the volume of the propellant system, and the fuel and binder occupy the void spaces between the relatively large oxidizer particles. The primary particles of the fuel are orders of magnitude smaller in size than the oxidizer particles, and this fact makes necessary that extensive time and energy be expended in shear mixing the various components of the blend to obtain the necessary degree of homogeneity. Quality control of the operation is difficult, and once binder curing agents are added to the blend, there is a limited amount of time available before the blend becomes solid and incapable of being moulded into pellets or other such shapes.
Prior to blending, the fuel particles, e.g., carbon or aluminum, are generally mixed or coated with a resinous binder to form an agglomerate. The agglomerate is generally formed by coating particles of the fuel with the resin dissolved in an organic solvent or by dry-blending the fuel with the binder. Representative prior art procedures are described below.